Conventionally, in automotive electrical components such as lamps and ECUs (Electrical Control Units) for automobiles, OA (Office Automation) equipment, home appliances, medical devices, etc., an opening is formed in a housing for accommodating electronic parts, a control board, etc. to reduce the pressure fluctuation in the housing or to ventilate the housing, and a ventilation member is mounted in the position where the opening is formed. This ventilation member not only ensures ventilation between the inside and outside of the housing but also prevents foreign substances from entering the housing.
For example, JP 2007-141629 A discloses a ventilation member as shown in FIG. 9. This ventilation member includes: a support body 12 for closing an opening 14a of a housing 14 with a gas permeable membrane 11 when the support body 12 is fixed to the housing 14; a cover body 15 mounted on the support body 12 to cover the gas permeable membrane 11; and a sealing element 13 for sealing between the support body 12 and the housing 14 at a position surrounding the opening 14a. 
Specifically, the support body 12 has a flange portion 12a and a cylindrical portion 12b. The gas permeable membrane 11 is attached to the front surface (upper surface in FIG. 9) of the flange portion 12a, and the back surface (lower surface in FIG. 9) thereof presses the sealing element 13 against the housing 14. The cylindrical portion 12b extends from the inner peripheral portion of the back surface of the flange portion 12a so as to be inserted into the opening 14a of the housing 14. Hooks 12c are formed on the edge of the cylindrical portion 12b and caught by the peripheral portion of the opening 14a from the inside of the housing 14.
The support body 12 shaped as mentioned above can be formed by, for example, injection molding. In this support body 12, however, the hooks 12c and the flange portion 12a overlap in the axial direction of the cylindrical portion 12b. Therefore, it is necessary for the injection molding to use both an axial die for forming the interior space of the cylindrical portion 12b and a pair of slide dies that can be separated from each other in the direction orthogonal to the axial direction of the axial die. In the injection molding using these axial die and slide dies, it is difficult to produce a large number of support bodies 12 at a time.